The register
The register lists Sendmarc Limited in London as a licensed sponsor on Global Business Mobility: UK Expansion Worker, an entry that goes back to at least 2026. Rating on the current register: Worker (UK Expansion Worker: Provisional).
Companies House lists the business as Sendmarc Limited, company number 17273202, a private limited company. Registered office: 5 Approach Road, London, SW20 8BA, SW20 8BA. By its SIC codes the business is in it, software and media.
A licence says an organisation may sponsor; it does not say it is hiring today. The way to find out is the same as for any employer: the careers page, the job boards, and a direct approach with a UK-style CV that says early that sponsorship would be needed.